Seo Kouji is a Japanese manga creator from Shobara, Hiroshima, Japan. He has stated in an interview that he was a member of his high school's track and field team and that he loves to watch baseball both emphasized in his hit manga Suzuka.

He debuted in 1996 with the one-shot "Half & Half" in Fresh magazine. His two hits, Suzuka and Cross Over, both mixed the genres of sports with high school romance. Suzuka focused on track and field while Cross Over used basketball. It is also interesting to note that the main love interest of the male protagonists of several of his works are extremely similar in appearance, namely in Half and Half, Cross Over, Suzuka, and Kimi No Iru Machi.

Seo was an assistant to Oushima Tsukasa, and studied under Fujio Fujiko and Soda Masahito.

In 2009 Seo designed the High School Girl Kimchi for Hokubi Construction food company.